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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Teacher  Overview  –  3  pages    

 

Balanced  and  Unbalanced  Forces  

 

Lesson  Created  by  

Carlos  Irizarry,  George  B.  Swift  Specialty  School,  Chicago,  Illinois  

Purpose    

To  fully  appreciate  and  make  a  connection  to  Newton’s  Laws,  students  must  explore  how   unbalanced  forces  cause  an  object  to  move.  Students  must  also  be  able  to  quantify  force  to   better  understand  the  nature  of  balanced  and  unbalanced  forces.    

 

Overview  

Students  will  use  the  Fourier  force  meters  to  investigate  the  net  force  of  a  sliding  block  and   observe  how  greater  unbalanced  force  results  in  greater  motion.    Students  will  also  observe   how  balanced  opposing  forces  create  net  zero  force  which  results  with  zero  motion.    

Students  may  also  explore  how  greater  or  lesser  weight  of  an  object  requires  greater  or   lesser  force  to  move  that  object.  Using  the  HP  force  meter  and  tablets,  students  are  able  to   record  their  observations  quantitatively.  Students  also  develop  force  diagrams  to  publish   their  findings.  

 

Student  Outcomes    

Illinois  State  Standards:    

• 11.A.3c:  Collect  and  record  data  accurately  using  consistent  measuring  and   recording  techniques  and  media.  

• 11.A.3f:  Interpret  and  represent  results  of  analysis  to  produce  findings.   • 12.D.3a:  Explain  and  demonstrate  how  forces  affect  motion.  

 

National  Science  Education  Standards:    

• 8ASI1.3:  Use  appropriate  tools  and  techniques  to  gather,  analyze,  and  interpret   data.  The  use  of  tools  and  techniques,  including  mathematics,  will  be  guided  by  the   question  asked  and  the  investigations  students  design.  The  use  of  computers  for  the   collection,  summary,  and  display  of  evidence  is  part  of  this  standard.  Students   should  be  able  to  access,  gather,  store,  retrieve,  and  organize  data,  using  hardware   and  software  designed  for  these  purposes.  

• 8ASI2.4:  Technology  used  to  gather  data  enhances  accuracy  and  allows  scientists  to   analyze  and  quantify  results  of  investigations.  

• 8BPS2.1:  The  motion  of  an  object  can  be  described  by  its  position,  direction  of   motion,  and  speed.  That  motion  can  be  measured  and  represented  on  a  graph.  

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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Teacher  Overview  –  3  pages    

Time  

One  45-­‐minute  class  period     Level  

8th  Grade  Physical  Science   Materials  and  Tools  

• HP  tablet  computer  

• HP  39gs  graphing  calculator  emulator  software   • HP  force  meter  (DT272)  

• HP  StreamSmart  400   • Multiple  weighted  blocks   • Rubber  bands  

• String,  yarn,  etc.      

Preparation  

• Test  all  force  meters  and  HP  tablets  and  make  certain  they  are  operational.     • Ensure  that  there  are  enough  materials  available  to  students  to  support  student  

autonomy.    

• Students  will  need  a  large,  flat  working  surface.     Prerequisites  

• Students  should  have  a  working  understanding  of  forces,  friction,  weight,  gravity,   and  resistance.    

• Force  diagrams  should  have  been  modeled  and  practiced  prior  to  this  activity.     Background  

Students  should  also  be  well  trained  in  using  the  HP  force  meter  and  gathering  data  on  the   HP  tablets.    

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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Teacher  Overview  –  3  pages    

 

Teaching  Notes  

• A  class  tug-­‐o-­‐war  activity  can  be  a  very  fun  and  powerful  activity  to  help  solidify   their  budding  understanding  of  these  concepts.    

• Weighted  blocks  can  be  substituted  for  any  other  materials  that  have  some  weight   and  small  resistance  to  moving.    

                                                                 

This  work  is  supported  by  a  grant  from  Hewlett-­‐Packard  under  the  HP  Catalyst   Initiative.  However,  any  opinions,  findings,  conclusions  and/or  recommendations  are  

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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Student  Guide  –  3  pages    

 

Balanced  and  Unbalanced  Forces  

Review:  

It  is  important  to  remember  that  force  can  be  described  as  a  push  or  a  pull.  When  

one  object  pushes  or  pulls  a  second  object,  one  can  say  that  the  first  object  is  

exerting  a  force  upon  the  second  object.  Much  like  when  a  soccer  player  kicks  a  

soccer  ball,  the  soccer  player  (the  first  object)  kicks  the  ball  (the  second  object)  

thereby  exerting  a  force  onto  it.  You  exert  a  force  whenever  you  lift,  turn,  carry,  

or  throw  something.  You  exert  a  force  even  when  standing  still!    

Remember:  what’s  the  force  that  is  always  exerted  upon  us  while  we  are  on  

Earth?  We  try  to  resist  this  force  every  time  we  stand,  walk,  run,  climb,  etc.    

Remember  also  our  discussion  on  balanced  and  unbalanced  forces.  When  the  

forces  put  upon  an  object  are  balanced,  the  forces  will  not  change  the  object’s  

motion.  However,  when  the  forces  are  unbalanced  the  object’s  motion  will  

change.    Remember  net  zero  force  means  zero  change  in  motion.  

 

How  is  standing  still  an  example  of  forces  in  balance?  How  is  falling  downstairs  an  

example  of  forces  that  are  unbalanced?  Do  NOT  demonstrate!  

 

Challenge:  

Today  we  will  explore  how  an  object’s  mass,  the  force(s)  exerted  upon  it,  and  the  

changes  in  its  motion  are  all  interrelated.    

Think  aloud  with  your  group…  

Does  the  amount  of  force  exerted  upon  an  object  affect  its  motion?  

How  does  changing  the  mass/weight  of  the  object  affect  the  amount  of  force  

needed  to  set  the  object  in  motion?  

 

 

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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Student  Guide  –  3  pages    

Procedure  1:  

1. Place  one  block  upon  the  table,  and  hook  two  force  meters  to  it  (one  to  

each  side  as  previously  demonstrated).    

2. Two  group  members  should  each  take  a  force  meter  and  pull  the  block  so  

that  it  reads  1  N  on  each  meter.    

3. Observe  the  block.  In  your  science  notebook,  draw  a  force  diagram  similar  

to  the  example  below.  On  your  force  diagram  record  the  forces  on  the  

block  from  Step  2.  Discuss  with  your  team  and  explain  in  your  notes  why  

the  block  is  not  in  motion.    

4. Have  one  group  member  gently  pull  the  block  with  the  force  meter  at  1.5  

N,  while  the  other  group  member  pulls  steady  with  the  force  meter  staying  

at  1  N.    

5. Observe  the  block.  In  your  science  notebook,  draw  another  force  diagram.  

On  your  force  diagram  record  the  forces  on  the  block  from  Step  4.  Discuss  

with  your  team  and  explain  in  your  notes  why  the  block  IS  in  motion.    

6. Give  other  members  of  your  team  the  opportunity  to  carry  out  Step  4  and  

observe  changes  in  motion  with  changes  of  force.    

7. Discuss  with  your  group:  Does  the  amount  of  force  applied  to  the  block  

change  its  motion  (direction  and  speed)?  Draw  conclusions  and  record  your  

group’s  thoughts  in  your  notes.    

8. Discuss  with  your  group:  Which  force  diagram  should  be  labeled  “Zero  Net  

Force”?  Which  force  diagram  should  be  labeled  “Non-­‐zero  Net  Force”?  

Which  diagram  shows  balanced  forces?  Which  diagram  shows  unbalanced  

forces?  

9. Label  each  diagram  accordingly.    

 

Force  Diagram  Template  

 

 

 

 

 

 

 

 

     

         Block  

____N  

____N  

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  ©  2011  Office  of  STEM  Education  Partnerships,  Northwestern  University     Balanced  &  Unbalanced  Forces  –  Student  Guide  –  3  pages    

 

Procedure  2:    

1. Have  one  group  member  attach  one  force  meter  to  the  ½  kilogram  block  

and  gently  increase  the  amount  of  force  used  to  pull  the  block  until  it  

begins  to  move.    In  your  science  notebook,  record  the  minimum  amount  of  

force  required  to  set  the  ½  kilogram  block  into  motion.  

2. Repeat  Step  1  using  the  1  kilogram  block.  

3. Repeat  Step  2  using  the  3  kilogram  block.    

4. Organize  your  information  into  a  clear  and  comprehensible  data  table  of  

your  own  design.    

5. Allow  all  members  of  your  group  the  opportunity  to  manipulate  the  blocks  

with  the  force  meters.    Discuss  your  observations.    

6. Think  and  discuss  with  group:  What  seems  to  be  the  relationship  between  

the  mass/weight  of  an  object  and  the  amount  of  force  required  to  set  it  in  

motion?  

7. Organize  your  thoughts  with  your  group  and  be  prepared  to  share  out  your  

group’s  theories.    Use  your  data  table  to  support  your  thinking.    

References

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